Portable radio device



Dec. 12, 1950 D. H. MITCHELL 2,533,493

PORTABLE RADIO DEVICE Original Filed Feb. 20, 1942 4 Sheets-Sheet 1 ,950 D. H. MITCHELL PORTABLE RADIO DEVICE '4 Sheets-Sheet 2 Original Filed Feb. 20, 1942 Dec. 12, "1950 D. H. MITCHELL PORTABLE RADIO DEVICE 4 Sheets-Sheet 5 Original Filed Feb. 20, 1942 ,jwmaw/wzigzz ILA-m 13% w 0119;

Dec. 12, 1950 D. H. MITCHELL PORTABLE RADIO DEVICE Original Filed Feb. 20, 1942 4 Sheets-Sheet 4 QM w n SEW S Mm ufi TRJ X WK @m %06/2 for. jazzaflfl/Vafcie/Z Patented Dec. 12, 1950 UNITED STATES ATENT OFFICE PORTABLE RADIO DEVICE Original application February 20, 1942, Serial No.

1946, Serial No. 673,219

3 Claims. (01. 250-13) The present invention relates generally to radio apparatus and in particular to a portable. selfcontained combination radio receiver and transmitter unit. This application is a division of copending application Serial No. 431,722, filed February 20, 1942, now Patent No. 2,439,408, dated April 13, 1948.

The combination portable radio receiver and, transmitter units now generally used are not entirely satisfactor because of their bulk and weight, and the conveniences encountered in setting them up for operation. In most instances these prior art sets are not self-contained as a.

package unit and usually include an earphone unit or an antenna unit which are separately at tachable to the body of the set by extension wires or the like. As a result these are not capable of operation immediately on reaching a new destination or while enroute to such destination, since some time must be used for assembling the earphone or the antenna units and for making various tuning and control adjustments. Further because of the bulk of the sets theyare difficult to handle and generally too heavy to be manually supported while in operation. In fact many of them require special supporting means upon which the various parts of the set are relatively arranged in a manner to facilitate their use. The maneuverability and the flexibility of application of these sets to the various field demands required of sets of this type, such asin any Army signal corps, police work and the like, is thus appreciably restricted. Even after the sets are'assembled for operation considerable delay is Divided and this application May 3-1,

intercoupling the electron discharge tubes of a. combined radio transmission and receiving system to provide either a signal receiving channel or a signal. transmitting channel.

It is another object of the invention to provide an improved arrangement for changing the resonant frequency of at least one of the tuned stages of the system, each time the switching apparatus is operated to change the character of the system.

It is still another and more specific object of the invention to so arrange the. available tubes of the system, the switching apparatus and the availablev circuit elements that an. eflicient signal receiving channel of the. super-heterodyne type is:

provided each time the switching apparatus is operated to condition the system for signal reception, and an efficient. transmission channel of themodulated carrier type, which utilizes a large proportion of the apparatus used in the receiving channel, is provided each time the switching apparatus is operated to condition the system for usually involved in the transmission and recep- 1 tion of signals because of the time lost in changing from transmitting to receiving and vice versa. Also because of their relatively complicated structure, the component parts of the prior art sets areusuallycompletely dismantled for servicing and It is an object of this invention, therefore, to.

provide an improved radioapparatus.

Another object of this invention is to provide an improved combination radio receiver and transmitter unit.

It is a further object of the invention to provide improved switching apparatus for selectivelysign al transmission.

A feature of the invention isthe provision of a facilities are provided for changing the charac-- teristics of the system antenna circuit, each time the switching apparatus is operated tochange the character of the system.

In accordance with another feature ofthein-" vention, provisions are made for changing the* biasing potentials applied to the input electrodes of at least a portion of the tubes, each time theswitching apparatus is operated to change the character-of'the system.

Still another feature of the invention is the provision of an improved arrangement for cou" pling the sound reproducing device of the system to the audiofrequency transmission channel eachtime the switching apparatus is operated toconedition the system for signal transmission.

A still further feature of this invention is the provision of a portable radio receiver and trans j mitter set, which is capable of being supported in one hand and. in but one position for eithertransmitting or receiving, and in which a manually operated switch for changing the set to oper ate as either a receiver or transmitter is ar-' ranged for manipulation by thehand supporting the set.

Further objects, features, and advantages of this invention will become apparent from the following description when taken in connection with the accompanying drawings in which:

Fig. 1 shows the complete radio receiver and transmitter unit of this invention supported for operation in but one hand of the operator;

Fig. 2 is a front perspective view of the radio unit of this invention as it appears when not in use;

Fig. 3 is a perspective view of the invention looking at one end thereof, with such one end being opened to show the relative arrangement of the chassis unit and battery units, which comprise all of the component operating parts of the radio unit, in a single housing structure;

Fig. 4 is a fragmentary sectional view showing the manually operated means for actuating the change-over switch means;

Fig. 5 is an elevational view of the chassis unit looking at one. end thereof and showing the clip means for retaining the receiver and transmitter crystals in assembly position;

Fig. 6 is a plan View of the chassis unit, the unit being shown in actual size;

Fig. 7 is a side elevational view of a transparent insulating member which forms a part of the switch means for changing the operation of the combination set of this invention from a receiver to a transmitter and vice versa;

Fig. 8 is a plan detail view of the change-over switch means;

Fig. 9 illustrates diagrammatically a complete circuit for the unit of this invention; and

Fig. 10 illustrates diagrammatically a circuit showing the connection of the filaments for the vacuum tubes in the diagram of Fig. 9.

In practicing this invention there is provided a portable self-contained combination radio receiver and transmitter set which is compact and light in weight so as to be easily carried about or supported in one hand. The set includes a chassis, battery, microphone and earphone units, each of which is of a preassembled construction and capable of separate assembly in or removal from a common housing. The housing has open ends which are closed by removable cover plates, the housing being divided into a plurality of longitudinally extending compartments for receiving corresponding ones of the chassis and battery units. On removal of the housing cover plates these units are immediately accessible for easy removal from the housing. The housing is of an elongated construction so that it can be readily grasped in one hand, the earphone and microphone units being relatively arranged thereon so that the set can be held in an operating position by the operator in a manner similar to that of the well known telephone set.

A single switch means is utilized to change the set over from operating as a receiver to a transmitter and vice versa. The switch means is assembled as a part of the chassis unit and is positioned entirely within the housing. A manually operated unit for actuating the change-over switch means projects outwardly from one side of the housing, and is arranged relative to the earphone and microphone units so as to be positioned below the one hand of the operator used in supporting the set in an operating position. It is necessary merely to press and release the changeover switch with such supporting hand to immediately change the set from a receiver to a trans mitter and vice versa.

Because the set is easily suported in one. hand to a common operating position for both receiving and transmitting, it is readily apparent that the set can be used at any time regardless of whether the operator has arrived at his destination or is still enroute to such destination. The operating portion for the switch means, the housing cover plates, and the earphone and microphone units are all in a waterproofed assembly relative to the housing so that the complete set can be submerged in water without injury thereto. Since the set is completely enclosed within a common housing structure it is capable of being subjected to considerable rough handling and abusive treatment without permanent injury thereto.

Referring to the drawings the combination radio receiver and transmitter set of this invention is illustrated in Figs. 2 and 3 as including an elongated housing 49 of substantially square cross section over its entire length and open at the ends 4| and42 thereof. In order to make the complete set as light as possible in weight it is contemplated that the housing 49 be composed of aluminum or like material. The housing 49 is divided longitudinally by partition members 43 and 44 into compartments for an A battery unit 49, a B battery unit 5|, and a preassembled chassis unit 52, respectively. The batteries 49 and 5| are the sole source of energy supply for the set. The batteries 49 and 5| have contacts 53 and 54, respectively, at one of their corresponding ends, which are positioned at the open end 4| of the housing 49. The contacts 53 and 54 are thus positioned in proximity to contacts 5B and 51 respectively, carried on an end wall 58 of the chassis unit. The chassis unit 52 is connected through jack connections 59 and GI -to an earphone unit 92 and a microphone unit 63 (Fig. 3), respectively. The wires 45 and 59 connecting the latter two units with the chassis 52 at the connections 59 and BI, respectively, are positioned in a space provided by an insulating spacing member 64 extended longitudinally of the B battery compartment 41.

The open end 4| of the housing 49 is closed by a door or cover plate 66 pivotally supported by hinge means 61 on the housing 4|! and having contact bridges 68 and 69 carried on the inside thereof. On closing of the cover 66 the contacts 53 and 51 are connected together by the bridge member 68, and the contacts 54 and 56 are connected together by the bridge member 69. Wires for connecting the batteries 49 and 5| with the chassis unit 52 are thus entirely eliminated. The cover 66 is releasably locked in its closed position by a swing bolt ll pivoted at 12 to the housing 40 and receivable within a slot 13 formed in a projection 14 on the cover 66. With the shank portion of the bolt H positioned within the slot 13, tightening of the nut 16 clamps the cover 66 against the open end 4| of the housing.

The chassis unit 52 is of a preassembled construction and is shown in Figs. 5 and 6 in actual size. The chassis unit 52 includes a frame member of substantially L-shape integrally formed with a base portion 89 and a supporting portion 9|. Carried in the supporting portion 9| and in a spaced relation longitudinally thereof are peanut vacuum tubes TIT5, inclusive. Also carried on the supporting portion 9| and extending transversely of the base portion 89 is a first IF transformer L4 positioned intermediate the tubes T2 and T3, and a second IF transformer L5 arranged between the tubes T3 and 7 irieml aer I93 of flat form and a movable insulating member I94 also of flat form and arranged for linear movement relative to the stationary member I93. Extending in linear alignment and arranged in a spaced relation longitudinally of the stationary member I93, are contacts I 96 having engaging fingers I9? and I98 (Fig. 4). As illustrated for the switch contact I96a in Fig. 8, the stationary member 193 is formed with an aperture I99 for receiving therein the finger portion I9? of the switch contact I96a. The finger portion I91 is thus retained substantially in the plane of the stationary member I93. It is to be understood, of course, that the above construction for the contact I990, is similar for all of the contacts I99.

The movable member I94 carries contactsZIlI of substantially L-shape havin a leg portion 292 extending through a corresponding slot 293 formed in the stationary member I93. The end 204 (Fig. 4) of the leg portion 292 is anchored in the movable member I94 so as to be retained in a fixed position thereon. A second leg portion 299 substantially normal to the leg portion 292 is projected laterally away from a corresponding slot 299 for positioning between'the fingers I91 and I98 of corresponding contacts I96. By virtue of the finger I9! being ubstan-- tially in the plane of the stationary member I93, the leg portions 296 are slidably supported for movement on the member I93 and through the finger portions I9? and I98 whereby to slidably support the movable member I 94 on the stationary member I93. It is seen, therefore, that on linear movement of the movable member I94 relative to the stationary member I93 the contacts 29I are moved relative to corresponding contacts I96 to control the energization of the circuits associated with the contacts I96. Contacts on the stationary member I93 not engaged by any contacts 29I on the slidable member I93 are indicated at 299. These contacts 290 are merely the lugs for other circuit connections.

The operation of the switch I92 is manually controlled by a manually operated unit 291 operatively supported on the housing 49 and to the outside thereof (Fig. 4). The unit 201 includes toggle or extensible means 299 comprising a pair of members 299 and 2!! of substantially arcuate shape which are pivotally connected together at their adjacent ends by axis means 2I2. The end I23 of the toggle member 2II is pivotally connected by axis means 254 with a bracket member 2H5 secured to the housing 40 by a screw or the like 211 so that the end 243 is in a fixed position relative to the housing 49. The end 258 of the toggle member 299 is pivotally connected by axis means 2i9 with a linearly movable member 22I which is slidably supported on the locus-- ing 49. The linear movement of the slidable member 22I is in the same direction as the linear movement of the movable member I94 of the switch I92, the member 22! having guiding rim portions 223 thereon for receiving a guiding member 224 secured by a screw 226 to the housing 49. On pressin the toggle means 298 toward the right, as viewed in Fig. 31, the pivotal connection 2 I2 between the toggle members 299 and 2I I is moved in an arcuate path which is substantially normal to the direction of linear movement of the slidable member 22| and hence to the direction of linear movement of the switch member I94. This movement of the toggle means 298 linearly moves the end 2| 8 ofthe toggle member 209 to in turn move the slidable member 22 I in a linear direction. The position of the parts of the manually operated unit 201 when the toggle means is in a depressed condition is shown in dotted lines in Fig. 31, The movement of the pivotal connection 2I2 i limited by a cushioned bumper 22'! carried on the housing 49 and secured thereto by the screw 2I'I.

The slidable member 22I has an extension 228 thereon which extends through an opening 230 formed in the housing 40. This extension 228 is in abutting engagement with a projection 229 secured to the movable switch member I94 and extending laterally therefrom through a slot 23I formed in the stationary switch member I93. On movement of the pivotal connection '2I2 to the right, as viewed in Fig. 4, the extension 228 on the slidable member 22I is moved downwardly to in turn engage the projection 229 for movement therewith to their positions shown in dotted lines in Fig. 4. This downward movement of the projection 229 in turn linearly moves the movable member I94 in one direction relative to the stationary member I93 and hence the contacts 20I relative to the contacts I99 to control the radio circuits.

On release of the toggle means 298 the toggle member 2| I is initially moved by a spring member 232 out of a binding position with the toggle member 299. The continued movement of the toggle mean 298 to its unoperated position is accomplished by a tension spring 233 (Fig. 8) connected at one end to the stationary member 593 and at its opposite end to the movable member 594, the spring being partially positioned :within a slot'234 formed in the stationary me.

ber I93. This action of the sprin member 233 linearly moves the member I94 in an opposite direction relative to the member I93, with the engagement of the projection 229 with the extension 228 on the slidable member 22I returningthe toggle means 299 to an idle position. When the manually operated unit 29'! is in the position indicated in full lines in Fig. 4, the set is connected for operation as a receiver. With the toggle unit 291 in the position indicated in "dotted lines in Fig. 4 the set is operated as a transmitter. It is seen, therefore, that changing the operation of the set from a transmitter to a receiver is automatically accomplished simply by releasing the operating unit 29? and that the set will operate as a transmitter so long as the unit 291 is retained in a depressed position. The change over from receiving to transmitting and vice versa is accomplished in a minimum of time and without any delay for making adjustments "between the receiving and transmitting operations.

The flat arrangement of the change-over switch means I92 longitudinally of the chassis unit 52 and across one side of the tubes TleT5, inclusive, provides for the contacts I93 and MI I corresponding to an associated tube being substantially adjacent such tube without projecting any appreciable distance laterally from the chassis unit 52. By virtue of a tube and its associated contacts being adjacent each other only very short leads or connections are required for connecting the contacts of the switch I92 into the tube circuits so as to substantially reduce the circuit losses resulting from long connections. A transparent insulating member 239 (Fig. 7) is arranged in a superposed relation with the switch unit I92 and is secured at each end thereof. to the radio chassis 52. The transparent insulating member 239 is adapted to have-applied thereon suitable markings, indicated as From a consideration of Figs. and 6, it is seen that the chassis unit 52 is completely constructed as a preassembled unit which is of a substantially rectangular cross section over the entire length thereof. All of the resistor and condenser elements for the various tube and circuit arrangements, the antenna I36 and the change-over switch I92, are relatively arranged so as to be confined within a space defined substantially by the transverse and longitudinal dimensions of a tube and associated socket portion. The chassis unit, including the change-over switch I92 and the antenna I36, is thus adapted to be removed from or inserted within the housing 40 as a complete and compact package. In connection with the insertion of the chassis unit 52 within the housing compartment 48 it is seen from Fig. 4 that the projection 229 on the change-over switch 4.92 is moved adjacent the extension 228 on the slidable member 22I. The extension 228 and the projection 229, therefore, do not in any way interfere with the assembly of the chassis unit 52 within the housing 40 and are completely operatively connected concurrently with the positioning of the chassis unit within the housing.

The operation of the set is best understood in connection with the circuit diagram in Fig. 9 which shows the complete circuit for the set. For the purpose of simplicity and clarity of description the change-over switch I92 will be considered as comprised of 14 section A-H, and J-O, both inclusive, and the parts of the control circuit will be described relative to their functions as controlled by these switch sections. It is to be understood of course that corresponding parts in all of the figures will be designated by like numerals of reference.

Referring to Fig. 9, the change-over switch I92 is shown in full lines in a position providing for the operation of the set as a receiver. In a receiving condition, the set acts as a five tube superheterodyne receiver consisting of one RF amplifier stage including the tube TI, one oscillator mixer stage including the tube T2, one IF amplifier stage including tube T3, one diode detector and first audio amplifier stage including tube T4, and one audio power output stage including the tube T5. With the change-over switch I92 in a position for receiving, the switch section A connects the crystal MI across the grid 300 and the screen grid 39I of the tube T2.

The connection of the crystal MI in this manner provides the necessary coupling for oscil ation. Section B connects a voltage divider V illustrated as comprised of three resistors across a resistor R4 to be later noted. This voltage divider V provides the grid bias voltage for the tubes TI, T2 and T5, the grids for these tubes being indicated at 302, 300 and 303', respectively. The switch section C connects the control grid 352 of the tube TI into the AVG circuit of the diode detector tube T4.

Switch section D connects the antenna I36 to the tuning condenser 01. The section E connects the plate 304 of the tube TI to the coupling condenser .CIO of the signal grid 300 of tube T2. The switch section F connects the oscillator feed-back condenser C6 to round. Section G puts the voltage dropping resistor RIB in series with the plate 304 of tube TI. Section H connects the B battery 5| to the plate 306 and screen grid 35'! of the tube T3. The section H also connects the plied to the grid 302 of tube TI 11-0 voltage dropping resistor RII in series with the plate '308 of tube T5.

The section J of the change-over switch I92 functions to ground the microphone unit 63 when the set is utilized for receiving. The switch section K connects the terminal A of the filament 309 of the tube'T3 to the A battery 49 and disconnects one section of the two-section filaments 3H and 3| 2 in the tubes TI and T5, respectively, from the A battery in a manner which will be later explained. The switch sections L and M are connected together electrically through contact 20]" on the movable switch member I94 -of the change-over switch I92. When contact 20I' is in its receiving position shown in full lines in Fig. 9, the dropping resistor RIB is connected in series with the screen grid 3| 3 of the tube T5. These switch sections L and M also place the dropping resistor R" in series with the screen grid 314 and 30I of tubes TI and T2, respectively, and connect the 3 battery 5I to the plate 304 of tube T'I.

*The sections N and O are electrically connected together through a second contact 20! of the change-over switch I92. The contacts 20I are substantially L -shaped, as shown in Fig. 8, for contact with two terminals I96 on the long portion and a single terminal I96 on the short portion thereof. These sections N and 0 place the earphone unit 62 across the audio choke L6 and the plate 308 of tube T5. The sections N and 0 also place the dropping resistor RI 9 in series'with the earphone unit 62 to reduce the intensity of the signal in'the earphone unit.

When the set is to be operated as a receiver the antenna I36 is series tuned by the mica trimmer C1. The signal voltage developed across C! is amplified by the tube TI and applied to the grid 300' of the tube T2. In the mixer oscillator tube T2, the incoming signal is mixed with the oscillator signal generated in the tube and produces a beat frequency plate current of 455 kc. The oscillator uses a crystal MI in a crystal circuit, previously noted, and functions at 455 kc., above the carrier or incoming signal frequency. For a particular frequency at which the set is to be operated the receiver crystal MI, therefore, is 455 kc., higher in frequency than the transmitter crystal M2.

The beat frequency or IF signal produced in the mixer tube T2 is amplified by the tube- T3 and is applied to the diode section 3I6 of the tube T4. Due to the detection process the modulated IF signal is demodulated, and an audio voltage is impressed across the resistor R20 which is the grid resistorof the pentode section,

or grid 3, of the tube T4. The signal is then applied to the grid 303' of the tube T5, the power amplifier, where it is further amplified and then applied to the earphone unit 62.

The inductance or antenna coil LI functions as a loading coil which aids in resonating the antenna I36. The grid resistor R2 of tube TI, provides a D. C. path for the bias voltage ap- The condenser C8 is an RF bypass for the circuit of the filament 3 of tube TI and functions to reduce regeneration. The condenser C2 bypasses the RF current from the screen grid 3I4 of tube TI. Bypassing of this RF current by the condenser C2 is rendered more effective by the resistor RIB which increases the impedance of the path through the B battery 5I. This arrangement is commonly called a decoupling filter. The resistor RI 8 also reduces the current fiow in the for grid 30!] being RI. vide the bias voltage for the grid 30!! of the oscillator and mixer tube T2 as well as the bias 1 of the circuit wiring for such tubes.

A coupling filter for the circuit of the plate v 304 of the tube Tl consists of the condenser C3 and resistor Rlfl. The resistor RID also serves to lower the D. C. plate voltage on the tubeTl which reduces its plate current and gives a more economical operation of the B battery. In

'other words the resistor RIB functions to decrease the current flow from the battery through the plate 304 of tube TI when the set I is operating as a receiver.

The condenser CH] in the circuit of the grid 350 for the tube T2 functions as a coupling con- ,denser for the passage of an RF current to the grid 30!], but prevents any D. C. plate voltage from tube Tl reaching the grid 360, the resistor Resistors R3 and R4 provo tage for the audio output tube T5. A D. C. voltage suitable for biasing purposes is produced .across the resistors R3 and R4 because of the grid current which exists as a result of driving the oscillator grid 303 positive. The vo tage di-,

vider V previously mentioned, .provides t e ,proper values of grid bias for the tubes Tl, T2 and T3 when necessary to reduce regeneration.

A filter for the automatic volume control ,(AVC) applied to the grids 302, 399 and 333 of the tubes Tl, T2, and T3. respectively, is comprised of condensers Cl3 and CIA and resistor R9. The AVC voltage is obtained from the de- ..tector load resistance made up of the resistors R13 and RM. The filter removes the audio component of the detector voltage from the D. C.

component which is used for the AVG function.

The condensers C5 and C23 function as bypass conden ers to prevent a voltage of the o cillator fre'yuency getting into the control grids 302 and 383' of the tubes TI and T5, respect vely, .through'the bias system. The conden er C4 is a neutral zing condenser.

It reduces the volta e of the oscil ator frenuencv on the signal grid 300 of tube T2, due to coupling within the. t"be,

.by feeding back a voltage of the oscillator frequency out of phase with the internal co p ed vo tage.

.cores and surrounded by an iron s eeve 322 to provide for the use of small coils of high inductance.

The coils 3!!! and 32l are tuned by the trimmers C and Cit, respectively. The resistor R8 which is contained within the iron shield 322 functions to broaden the response of the transformer.

Condensers Cl! and resistor R42 make up a decoupling filter for the screen grid of the tube T3. A decoupling filter for the plate circuit of tube T3 is comprised of condenser CH! and the resistor RIB. A second IF transformer L5 is comprised of primary and secondary coils 323 and 324, respectively, wound on corresponding iron cores and surrounded by an iron sleeve "l2 326,9. trimmer condenser Cl9 being used to tune the secondary winding.

The resistor Rh; is the detector load across which the audio voltage is obtained. Resistor Rl3 in conjunction with condensers C29 and (325i make up a filter to remove the IF component from the audio component of the detector voltage. The condenser C22 couples the detector to grid 3|! of tube Ti and prevents the D. C. component of the detector voltage from biasing-this grid 3 I i. The grid resistor R23 of the tube T l has a resistance of 10 million ohms so that the small amount of grid current which exists in the tube T6 and flows through this resistor provides additional bias for this tube on large signal inputs. The condenser C25 is an IF bypass to eliminate any IF current which exists in the circuit of the plate 32 of tube Ti from getting into the audio plate load resistor R22 for the tube T5. The condenser C25 and resistor R21 make up a decoupling filter for the screen grid 328 of the tube T l. Resistor R22 is the plate load for the tube T4, and C2? is the coupling condenser.

Resistor R23 is the grid resistor of tube T5. The condenser C28 and resistors R2 1 and RIB serve as a decoupling filter for the screen grid 3l3 of the tube The res'stor Rlfi also helps 7 reduce the current drain on the B battery 5! by lowering the voltage on the screen grid BIS. A low resistance D. C. path for the plate current in tube T5 is provided by the audio choke L5 which also ofiers a high impedancepath to the audio plate current. A decoupling filter for the plate 368 of the audio amplifying tube T5 is provided by the condenser C38 and resistor RI i. The resistor-RH also serves as a dropping resistor to lower the voltage in the plate 388. A condenser C2 6 prevents the D. C. plate voltage from reaching the earphone unit 62.

The circuit for the filaments 3i i, 33!, 339, 332 and 3l2 for the tubes Tl-T5, inclusive, when the set is operating as a receiver is shown in Fig. 10. The filament terminals indicated as :c and y, and the A battery termnal Xa correspond to the like terminal references in Fig. 9. As previously mentioned the filaments 3H and 352 for tubes Ti and T5, respectively, are of two-section type, the filam nt 3!! including sections 333 and 334, and the filament 3l2 including seztions 335 and 33?. With the switch section K in a postion for a receiving operation of the set the single section filaments 33L 389, and 332, and only the filament sections 333 and 335 of filaments 3! a and 3E2, respectively, are connected to terminal Xa for receiving energy from the A battery 49, the circuit for the filament sections 334 and 331 being open at the switch K. By virtue of this arrangement of the filament circuit the drain on the A' battery 49 is reduced for receiving operation when current requirements for efiicient signal reception are less than the current requirements for efiicient signal transmission. The energy of the A battery is thus conserved during receiving so as tobe available for the increased requirements in transmitting.

Referring to Fig. 9 the positions of the switch sections A-H, and J-O, both inclusive, are shown in dotted lines in the positions they occupy when the set is operated as a transmitter. When the combination set is operating as a transmitter only four tubes are used, the IF amplifier tube T3 being eliminated. The tube TI for transmitting acts as an RF power amplifier tube, the tube T2 as an oscillator, tube T4 as a microphone amplifier, and tube T5 as a modulator. Section A con- .n'ects'the transmitter crystal M2 with the screen grid 39! of the oscillator tube T2 in a crystal circuit arrangement. The section B of the "changeover switch I92 disconnects the voltage divider V which, when the set was being operated as a receiver, provided the grid bias voltage for the tubes Ti and T2 and T3. Switch C connects the control grid 302 of tube T! to the grid leak resistor R6. The section D connects the antenna 535 to the plate 3% of the RF amplifier tube Tl, while the switch section E connects the plate 304 to the RF amplifier tank condenser C42. The section F connects the condenser C6 to the oscillator grid 302 of the tube T2, and section G shorts out the resistor R10 from the plate 304 of the tube Ti. Section H disconnects the B battery 5! from, the plate 306 and screen grid 30'! of the tube T3 and also shorts out the resistor RH from the circuit of the plate 3030f the tube T5. The switch section J connects the microphone unit 53 to the grid 3|! of the first audio amplifier tube T4. Section K operates to disconout of the screen grid circuits of tubes Ti and T2.

The connected switch sections N and connect the screen and plate circuits of the RF am-- plifier tube TI to the plate 308 of the modulator tube T5.

When the set is operating as a transmitter the RF carrier is generated in the oscillator section of the tube T2. The crystal M2 used for transmitting operates at a frequency which is 455 kc. lower than the frequency of the crystal Ml used when the set is operating as a receiver, as was previously noted. The generated RF signal is applied to the grid 392 of the tube TI where it is amplified and fed into the antenna I36. The antenna is coupled to the amplifier tank or tuned circuit by an impedance matching network of the Pi type in which the capacity between the antenna rod and housing makes up one shunt branch. The microphone output is amplified by the pentode section 3!! of tube T4 and then applied to tbegrid 303 of tube T5 Where it is further amplified. The output of tube T5 is then fed into the plate circuit of tube Tl of the RF amplifier. It is to be noted that since the screen grid 3? of tube TI is tied to the lower end of coil L2 that the modulating voltage is in roduced into the screen grid circuit as well as the plate circuit. This arrangement improves the percentage and quality of modulation. The earphone unit 62 is also connected across the audio ou put so that the operator can hear what he is saying. This arrangement is referred to as a sidetone. When the tube T2 is operating in the transmitter circuit only the oscillator section thereof is utilized. The resistors R3 and R4 make up the grid leak which provides the bias voltage for the oscillator grid 302'. The D. C. voltage developed across R4 is us d also for the grid bias for the modulator tube T5.

The RF choke L3 provides a shunt feed arrangement for the screen grid 30I of the oscillator tube T2, with the condenser C6, determining the amount of feed back to the grid. A circuit bypass for the screen grid 30! of tube T2 is provided by a condenser Cll. Condenser C9 ing inductance.

functions as "a coupling condenser and provides a path for the RF current to the grid 302 of the RF power amplifier Tl, but prevents the D. C. screen grid voltage from being applied to the grid 392. The resistor R6 is a grid leak and provides the bias voltage for the grid 3c2. An RF bypass for the screen grid 3% of tube TI is provided by the condenser C2. The coil L2 serves as an :RF amplifier tank coil and CIZ as an RF amplifier tank condenser. The condenser Cl2 also acts as one branch of the Pi network connecting the antenna 36 to the amplifier tank. The capacity between the antenna rod and the housing acts as the other shunt branch of the Pi network. The antenna coil Ll is the series branch 2 as a load resistor for the microphone unit 63. A 25 decoupling filter for the screen grid 328 of tube T4 consists of the resistor R2! and condenser C26. Resistor R2! also serves to obtain the proper operating voltage on the screen grid, with the resistor R22 furnishing the plate load. Condenser C21 functions as a coupling condenser, and R23 as the grid resistor of the tube T5. The decouppling filter for the screen grid 3!,3 of tube T5 is comprised of the condenser C29 and resistor R24. Condenser C28 produces a low impedance path around then odulator choke L6 for the curr nt or the carrier frequency. This i necessary since th RF amplifier tank and modulator choke are connected in series. A low resistance path to the D. C. plate current of the modulator tube T5 and RF- amplifier tube TI is accomplished by the modulator choke L5 which ofiers a high impedance load to the audio frequency plate current of the modulator.

Overloading of the monitoring earphones is prevented by the resistor R19, since the audio output for modulating the amplifier is quite high. A condenser C24 removes the D. C. plate voltage of the tube T5 from the earphones, while condensers C3! and CH are B battery bypasses, It is to be noted that the condensers cs,

C13, CM, C23 and C25, and resistors Rl, R9, Hi3, B14 and the resistors of the voltage divider V are -Witi'10llt use when the set is operated as a transmitter, their functions when the set is operated as a receiver having been previousl explained.

' The circuit arrangement of the filaments 3H, 33!, 309, 332 and 3i2 for the tubes Tl-Trl, inclusive, for transmitter operation is apparent from Fig. 10, the switch K being in the dotted position. The filament 309 of the IF amplifier tube T3 is open at the switch K since this tube is not utilized for transmitting. However, the remaining filaments, including both sections of each of the filaments 3! I and 3 I2 are in series connection with the A battery 50 that tubes Tl, T2, T4 and T5 are operated at maximum output for transmitter operation.

From a consideration of the above description and drawings, therefore, it is seen that the invention provides a combination radio receiver and transmitter set which is of a very compact construction, light in weight, and which is completely self-contained as to the antenna, source of energy supply, and all of the necessary operatingcomponent-parts. In the commerclal embodiment hereinbefore referred to, efficient communication is attained over distances of approximately one to five miles depending upon the ground resistance. assembled into a minimum number of complete units to provide for the individual assembly and removal of these units relative to the housing therefor as separate packages. These various preassembled units may be kept in stock and bements are required for the sets while in service,

and only a single switch is utilized for changing the set from transmitting to receiving and vice versa. Because of this simplicity in construction, assembly, and operation of the set, it may be readily operated efiiciently by an unskilled operator. It is to be noted also that the combination set is immediately operative on turning on of the energy supply switch so that communications may be carried on while the operator is enroute to a destination or after he has arrived at such destination.

Although the invention has been described with specific reference to a particular embodiment thereof, it is to be understood that it is not to be so limited, since changes in the parts and in their relative arrangement can be made therein which are within the full intended scope of this invention as defined by the appended claims.

I claim:

1. A combined radio transmitting and receiving system comprising, a plurality of electron discharge tubes individually provided with cathodes, circuit means for interconnecting said tubes as a radio transmitting system, electrical means for energizing said cathodes of said tubes to heat the same for providing emission therefrom at a predetermined rate, and switching means coupled to said circuit means and to said electrical means for selectively changing the connection between said tubes to provide a radio receiving system, said switching means cooperating with said electrical means for reducing the heating energy supplied to said cathode of at least one of said tubes to thereby reduce the emission from said cathode of said one tube in response to operation of said switching means to condition said system for receiving. I

2. A self contained radio transmitting and receiving device comprising a plurality of vacuum All of the parts of the set are pre- 16 tubes having cathodes, at least one of said tubes having a cathode including two separately energized sections, a source of current for said cathodes, circuit means for interconnecting said tubes and said source of current for operation thereof as a radio transmitter, and switching means coupled to said circuit means for changing the connection between said tubes to provide operation thereof as a radio receiver, said switching means connecting said source of current to both sections of said cathode of said one tube for operation of said device as a radio transmitter and connecting only one section of said cathode of said tube to said source of current when said switching means is operated for signal reception. 3. A combined radio transmitting and receiving system comprising, a plurality of electron discharge tubes individually provided with cathodes, circuit means for interconnecting said tubes as a radio transmitting system, said circuit means including a tuned circuit to determine the frequency of the signal transmitted, electrical means for energizing said cathodes of said tubes for heating. the same and thereby providing emission therefrom at a predetermined rate, and a single switching means coupled to said circuit means for selectively changing the connection between said circuit means and said tubes to provide a radio receiving system and to increase the resonant frequency of said tuned circuit for signal reception, said switching means also being coupled to said electrical means and cooperating therewith to reduce the heating energy supplied to at least a portion of'said cathodes and thereby reduce the emission thereof in response to operation of said switching means to condition said system for signal reception.

" DONALD H. MITCHELL.

REFERENCES CITED I The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,735,344 White Nov. 2, 1929 1,940,881 Ports Dec. 26, 1933 1,973,298 Sloggett et a1. Sept. 11, 1934 2,018,569 Pettengill et a1 Oct. 22, 1935 2,106,159 Runge Jan. 25, 1938 2,223,049 vReichle Nov. 26, 1940 2,259,690 Hansen et al Oct. 21, 1941 2,288,214 Summers June 30, 1942 2,317,547 McRae Apr. 29, 1943 FOREIGN PATENTS Number Country Date 430,408 Great Britain June 18, 1935 470,366 Great Britain Aug. 13, 1937 627,045 France Jan. 3, 1938 

